1. Field of the Invention
The present invention relates to a valve timing control apparatus for variably controlling at least one of intake valves and exhaust valves of an internal combustion engine, in accordance with an operation state of the engine.
2. Description of the Related Art
Various valve timing control apparatuses have been put into practice which change valve timings of intake valves and exhaust valves in accordance with an operation state of an internal combustion engine. Further, Japanese Patent Publication Laid-Open No. HEI 9-324613 discloses a valve timing control apparatus employing vanes equipped with a lock pin. The outline of the valve timing control apparatus disclosed in this publication will be described with reference to FIGS. 11 and 12.
FIG. 11 schematically shows the structure of the valve timing control apparatus. As shown in FIG. 11, the valve timing control apparatus is composed of a variable valve timing mechanism (VVT) 212, an oil control valve (OCV) 240, an engine control unit (not shown) and the like. The engine control unit drive-controls the OCV 240 in accordance with operation control of the engine, thereby variably controlling the VVT 212.
FIG. 12 shows in cross section the structure of the VVT 212. The VVT 212 is provided on an intake-side cam shaft 211 (FIG. 11). The VVT 212 is composed of a housing 216 integrated with a sprocket 217, a rotor 219 incorporated in the housing 216 and the sprocket 217, a rear plate 214 (FIG. 11), and a front cover 220 (FIG. 11) for covering a front face of the housing 216. The rotor 219, the rear plate 214 and the like are coupled to the intake-side cam shaft 211 by means of bolts or the like such that they can rotate integrally. Further, as shown in FIG. 12, the rotor 219 is provided with four vanes 224 that are arranged at equal intervals along an outer circumference thereof and project radially.
On the other hand, in the aforementioned VVT 212, the sprocket 217 has a substantially cylindrical shape and is disposed on the outer circumference of the rear plate 214. The sprocket 217 is supported such that it can rotate relative to the rear plate 214 and the intake-side cam shaft 211. The sprocket 217 is drivingly coupled to a crank shaft (not shown). When the engine is started (comes into operation), the sprocket 217 rotates clockwise in FIG. 12 in response to rotation of the crank shaft.
Further, the housing 216, which is integrated with the sprocket 217, is provided with four protruding portions 225, which are arranged at equal intervals. Four concave portions 226 are provided to accommodate the vanes 224 of the rotor 219, and each of the concave-portions 226 is formed between adjacent ones of the protruding portions 225. With each of the vanes 224 being disposed in a corresponding one of the concave portions 226, an advancement hydraulic chamber 230 and a retardation hydraulic chamber 231 are formed on opposite sides of each of the vanes 224.
In a state where oil is supplied to both the hydraulic chambers 230 and 231, the rotor 219 and the sprocket 217 are coupled to each other at a relative angle corresponding to a pressure balance of the oil. In response to rotation of the sprocket 217, the rotor 219 and the cam shaft 211 are rotated.
If the pressure in the retardation hydraulic chamber 231 becomes higher than the pressure in the advancement hydraulic chamber 230, the vanes 224 rotate counterclockwise in FIG. 12. Then, each of the vanes 224 comes into abutment on one of the inner walls of a corresponding one of the protruding portions 225. In this state, the cam shaft 211 is in its most receded position with respect to the crank shaft. At this moment, the valve timing of intake valves (not shown), which are driven in response to rotation of the cam shaft 211, is also most retarded. Conversely, if the pressure in the advancement hydraulic chamber 230 becomes higher than the pressure in the retardation hydraulic chamber 231, the vanes 224 rotate clockwise in FIG. 12. Then, each of the vanes 224 comes into abutment on the other of the inner walls of a corresponding one of the protruding portions 225. In this state, the cam shaft 211 is in its most advanced position with respect to the crank shaft. At this moment, the valve timing of the intake valves (not shown), which are driven in response to rotation of the cam shaft 211, is also most advanced.
The VVT 212 is provided with a lock mechanism employing a lock pin. This lock mechanism will now be described.
As shown in FIG. 12, an accommodation hole 232, which extends parallel to the axis of the cam shaft 211, is formed in one of the protruding portions 225 within the housing 216. A lock pin 233 is slidably accommodated in the accommodation hole 232. A lock recess portion 234 (FIG. 11), which is opposed to the accommodation hole 232, is formed in the rear plate 214.
Further, a ring-like hydraulic chamber 249 is formed in the accommodation hole 232. The pressure of the oil supplied to the hydraulic chamber 249 acts on the lock pin 233. For this purpose, the oil supplied to the advancement hydraulic chamber 230 or the retardation hydraulic chamber 231 is used. The lock pin 233 is constantly urged in such a direction as to engage the lock recess portion 234 by a spring 235, which is interposed between the lock pin 233 and the front cover 220.
Accordingly, in the case where the force acting on the lock pin 233 based on an oil pressure becomes smaller than an urging force of the spring 235, for example, in stopping or starting the engine, the lock pin 233 engages the lock recess portion 234 of the rear plate 214 at a predetermined angle relative to the sprocket 217. At this moment, the sprocket 217 is mechanically coupled to the rear plate 214. Then, the rotor 219 and the sprocket 217 rotate integrally, for example, at a predetermined relative angle xcex2 as shown in FIG. 12. That is, each of the vanes 224 is advanced from the most retarded position by the predetermined angle xcex2.
On the contrary, in the case where the force acting on the lock pin 233 based on an oil pressure becomes greater than an urging force of the spring 235, for example, during operation of the engine, the lock pin 233 is released from the lock recess portion 234. Then, relative rotation between the sprocket 217 and the rear plate 214, namely, between the sprocket 217 and the rotor 219 is permitted.
In this valve timing control apparatus, the relative angle between the rotor 219 and the sprocket 217 at the time of engagement of the lock pin 233 with the lock recess portion 234 is selected so as to correspond to a valve timing that does not adversely affect startability of the engine. By selecting the relative angle between the two members, as it were, as an intermediate phase, the variable valve timing zone can be enlarged in response to assurance of startability of the engine.
In this manner, by setting the phase between the rotor 219 and the sprocket 217 at the time of engagement of the lock pin 233 with the lock recess portion 234 to the aforementioned intermediate phase, desirable characteristics of the valve timing control apparatus such as assurance of startability of the engine, enlargement of the variable valve timing zone, and the like can be obtained. However, an apparatus that performs the aforementioned phase control or operation control of the lock pin 233 using a hydraulic pressure in the engine cannot avoid the following inconveniences.
That is, according to the aforementioned valve timing control apparatus, in a state where the hydraulic pressure is low in stopping or starting the engine, appropriate engagement of the lock pin 233 cannot be achieved. In other words, the controllability in the aforementioned intermediate phase deteriorates significantly.
It is an object of the present invention to provide a valve timing control apparatus for an internal combustion engine that can enhance controllability in an intermediate phase even when stopping or starting the engine with certainty.
In a first aspect of the present invention, there is provided a valve timing control apparatus for an internal combustion engine which includes a rotational body, a cam shaft, a hydraulic chamber, a hydraulic pressure control system, a lock mechanism and a lock mechanism control system. The rotational body is drivingly coupled to an output shaft of the internal combustion engine. The cam shaft drivingly opens and closes valves of the internal combustion engine. The hydraulic chamber changes a rotational phase between the output shaft and the cam shaft through supply of a hydraulic pressure. The hydraulic chamber is formed between the rotational body and the cam shaft. The hydraulic pressure control system controls the hydraulic pressure supplied to the hydraulic chamber. The lock mechanism maintains the rotational phase between the output shaft and the cam shaft in a predetermined intermediate phase through a force other than the hydraulic pressure. The lock mechanism control system drivingly controls the lock mechanism.
In this construction, the control for driving the lock mechanism, namely, for preventing and allowing relative rotation between the output shaft and the cam shaft is performed independently of the hydraulic pressure control for controlling the rotational phase between the output shaft and the cam shaft. Therefore, even in the case where the hydraulic pressure in the internal combustion engine becomes unstable, for example, when stopping or starting the vehicle-mounted engine, the control for maintaining the intermediate phase can be suitably performed by driving the lock mechanism with a high degree of reliability. Accordingly, the engine can be stopped or started at predetermined valve timings.
In the aforementioned aspect, the lock mechanism control system may be designed to electrically drive-control the lock mechanism.
In this construction, the lock mechanism is electrically drive-controlled. Therefore, even in the case where the hydraulic pressure becomes unstable, for example, when stopping or starting the vehicle-mounted engine, the control for maintaining the intermediate phase can be suitably performed by driving the lock mechanism with a high degree of reliability.
Further, in the aforementioned first aspect, the lock mechanism control system may be designed to drive-control the lock mechanism through a hydraulic pressure control system that is provided separately from the hydraulic pressure control system.
In this construction; the lock mechanism is drive-controlled through a hydraulic pressure control system that is provided separately from the hydraulic pressure control system. Therefore, even in the case where the hydraulic pressure becomes unstable, for example, in stopping or starting the vehicle-mounted engine, the control for maintaining the intermediate phase can be suitably performed by driving the lock mechanism with a high degree of reliability.
In a second aspect of the present invention, there is provided a valve timing control apparatus for an internal combustion engine including a rotational body, a cam shaft, a hydraulic chamber, a hydraulic pressure control system, a lock mechanism and an electric stopper. The rotational body is drivingly coupled to an output shaft of the internal combustion engine. The cam shaft drivingly opens and closes valves of the internal combustion engine. The hydraulic chamber changes a rotational phase between the output shaft and the cam shaft through supply of a hydraulic pressure. The hydraulic chamber is formed between the rotational body and the cam shaft. The hydraulic pressure control system controls the hydraulic pressure supplied to the hydraulic chamber. The lock mechanism maintains the rotational phase between the output shaft and the cam shaft in a predetermined intermediate phase through a force other than the hydraulic pressure. The electric stopper selectively restrains relative rotation between the cam shaft and the rotational body in the predetermined intermediate phase so as to assist retainment of the intermediate phase by the lock mechanism.
This construction is provided with the electric stopper for selectively restraining relative rotation between the cam shaft and the rotational body in the predetermined intermediate phase so as to assist retainment of the intermediate phase by the lock mechanism. Thus, the locking operation can be reliably performed by means of the lock mechanism, and the aforementioned intermediate phase can be suitably controlled.
The electric stopper makes it possible to set the lock pin opposed to its engagement hole and to ensure engagement of the lock pin thereinto.